The baculoviruses are large DNA viruses distinguished by their prolific multiplication in host insects. Due to their unique properties, these pathogens are used as vectors for foreign gene expression, potent biological insecticides, and gene transfer vehicles. To ensure their replicative success, baculoviruses use novel mechanisms that expedite viral gene expression and suppress host defenses, including cell death by apoptosis. It is the long term goal of this project to investigate the molecular interactions between baculoviruses and their host cell by defining the mechanisms by which Autographa californica nucleopolyhedrovirus (AcMNPV) regulates gene expression and modulates the host apoptotic response. In an integrated series of experiments that use biochemical, genetic, and cell biology approaches, the molecular mechanisms by which early AcMNPV transcriptional regulators accelerate replication will be investigated. The mechanism of enhancer-mediated transcriptional activation by the immediate early transregulator IE1 will be determined by using new loss-of-function mutations and dominant inhibitors. These dominant inhibitors will be used in combination with interfering RNA (RNAi) to define the roles of IE1 during infection, including the induction of apoptosis. AcMNPV-infected insect cells will be used as a powerful yet convenient system to define the molecular signals by which DNA viruses trigger apoptosis. Capitalizing on the finding that AcMNPV induces widespread apoptosis in cultured Drosophila melanogaster cells, we use dominant inhibitors, RNAi, and the baculovirus apoptotic suppressors (p35, p49, and iap) to investigate the viral and cellular apoptotic factors in this model organism for which many of the cell death components are known. These studies will be complemented by a characterization of the molecular signals (viral and host) responsible for nodavirus-induced apoptosis in Drosophila. Collectively, these studies are expected to provide important insight into the highly conserved pathways of apoptosis, which contribute significantly to the pathogenicity of human viruses. In addition, the molecular mechanisms by which baculoviruses regulate early gene transcription are directly relevant to insect vectors of human disease.